An example of a pull factor would be

Natural disasters, political revolutions, civil war, and economic stagnation are all reasons why people might want to migrate away from a certain area. Job placement, however, is an example of a “pull factor,” something that makes an individual want to migrate to a certain area

Explanation:

they have different colored collars

union blockade

explanation:

the union blockade in the american civil war was a naval strategy by the united states to prevent the confederacy from trading.

the blockade was proclaimed by president abraham lincoln in april 1861, and required the monitoring of 3,500 miles (5,600 km) of atlantic and gulf coastline, including 12 major ports, notably new orleans and mobile. those blockade runners fast enough to evade the union navy could only carry a small fraction of the supplies needed. they were operated largely by british citizens, making use of neutral ports such as havana, nassau and bermuda. the union commissioned around 500 ships, which destroyed or captured about 1,500 blockade runners over the course of the war.